I made a scenario where the AI could either land units near city A, that was closer (movement-wise) and smaller (population-wise) to the AI capital (and Navy), than city B. I found the AI will land units at City A instead of at B, even when B was an undefended city and A was a defended town. When A was defended, the AI would ignore it and march to the capital, when it was undefended the AI would take it first. Obviously this is just a start to research, on a very basic set-up map to boot. City A was distance 6 from the AI capital, but only 4 moves (4 tiles east). City B was distance 5 and 5 moves (5 tiles SE).